Although many methods are known, as electrophotography, a method in which an transferred object is obtained by forming an electric latent image (electrostatic latent image) on a photosensitive member by various means utilizing a photoconductive material, next, developing the latent image using a toner, and if necessary, transferring the toner image on a transfer material such as paper, and subsequently, fixing the toner image by means of heating, pressing, hot pressing, or a solvent vapor, and remaining developer which is not transferred on the photosensitive member is cleaned by means of various methods, and the above-mentioned steps are repeated is generally used.
Among those, as a development system, an one component developing system is used preferably, because a developing machine of the system has a simple structure, few troubles, long life, and is easily maintained.
In such a developing system, the quality of a formed image depends largely on the performance of a magnetic toner. In the magnetic toner, a great deal of fine powder-like magnetic iron oxide is mixed and dispersed, and a part of the magnetic iron oxide is exposed on the surface of the magnetic toner. For this reason, the kind of the magnetic iron oxide influences the fluidity and the triboelectric charging characteristic of the magnetic toner, and, as a result, influences various characteristics required to the magnetic toner, such as the magnetic toner developing property and durability. Therefore, previously, with regard to the magnetic iron oxide contained in the magnetic toner, a great number of proposals have been performed.
As magnetic iron oxides, a magnetic iron oxide has been known, which contains Si and has a specified Fe/Si atom ratio on the surface of the magnetic iron oxide, and which has been subjected to a surface treatment with Al further (Japanese Patent Application Laid-Open No. H07-175262). According to such a magnetic iron oxide, although a toner could have excellent fluidity and could have stable charging characteristic even under high temperature and high humidity, problems in image quality such as a ghost and scattering due to the charging characteristic in a high-speed developing system have not been improved yet, resulting in room of improvement.
Moreover, as magnetic iron oxides, a magnetic iron oxide has been known, which contains Al and has been subjected to a hydrophobizing treatment and thereby has a specified magnetic properties (Japanese Patent Application Laid-Open No. H07-271089). In these magnetic iron oxides, a part or all of trivalent iron ions are replaced with Al, and the saturation magnetization value thereof is thus low. By using such magnetic iron oxides, a toner can be obtained, where magnetic cohesive force acting between toner particles is weak and the consumption amount of the toner can be thus reduced. Moreover, a toner can be obtained, which has a good shelf life even under high temperature and high humidity environment and can maintain sufficient image density and for which occurrence of fogging and tailing is suppressed. Moreover, since the amount of covalent irons and the amount of FeO in magnetite are maintained, it is possible to provide a magnetic toner whose degree of blackness is good. However, with regard to degradation of image quality due to unevenness of charging when it was used for a long period of time and instability of image quality under a low temperature and low humidity condition, they have not been investigated sufficiently.
In magnetic iron oxides, a magnetic iron oxides have been known, which contains Si element and Al element and has a specified Si and Al content ratio on the magnetic iron oxide surface (Japanese Patent Application Laid-Open No. H08-272136). By using such a magnetic iron oxide, a toner can be obtained, where the controllability of electrification thereof can be enhanced more than ever before, and, even in case of continuous image formation under a low temperature and low humidity environment, homogeneity of coating on a toner carrier is excellent. And, when such a magnetic toner is used, even in a solid image, image defects such as a thin spot/wave-like irregularity, are suppressed, thus enabling to obtain a high definition and sharp image. However, with regard to the stability of the image density under a high temperature and high humidity environment, has no been sufficiently investigated.
Moreover, as magnetic iron oxides, a magnetic iron oxides has been known, which contains one or more elements selected from the group of elements consisting of Li, Be, B, Mg, Al, Si, P, Ge, Ti, Zr, Sn, and Zn (Japanese Patent Application Laid-Open No. H10-073950). Such a magnetic iron oxide is excellent in the dispersibility into binder resin, and can stabilize the electrification characteristic of a toner. In addition, in the recent trend of decreasing particle size of the toner, excellent charging uniformity can be achieved even when a toner whose average particle size is equal to or smaller than 10 μm is used, the cohesiveness of the toner is also reduced, and high image density can be achieved, thus enabling to achieve image formation excellent in developing performance, where fogging is suppressed. However, with regard to improvement in the dot reproducibility and reduction of tailing from a viewpoint of electrification characteristic, and improvement of environmental stability, they have not been sufficiently investigated.
As magnetic iron oxides containing a different kind of element, a magnetic iron oxide has been known, which contains one or more elements selected from the element group consisting of Mg, Na, K, Ca, Li, Ti, S, Al, Si, B, and C outside the central part thereof, and whose true specific gravity at 20° C. is greater than 4 and smaller than 5.2 (Japanese Patent Application Laid-Open No. 2000-335920). In such a magnetic iron oxide, balancing of magnetic properties is good, true density thereof is small, and mixing performance thereof with resin is also good. In addition, when it is used for magnetic toners, a magnetic toner can be obtained, which provides high image density, and little fogging, and has a few magnetic iron oxide particles dropping out of toner particles. However, with regard to improvement of image quality and environmental stability, there has been room of investigation.
Moreover, a magnetic material has been known, which contains one or more metal elements selected from the element group consisting of Co, Ni, Cu and Zn together with Al, and in which the content of the metal elements and the ratio between total Al quantity contained in the magnetic iron oxide and Al quantity present on the surface of the magnetic iron oxide are specified (Japanese Patent Application Laid-Open No. 2002-169328). By using such a magnetic iron oxide, a magnetic toner which is excellent in fluidity, and can provide stable developing performance, and where toner fusion to a photoreceptor hardly occurs in long-term use can be obtained. However, in order to improve phenomena in image quality such as a ghost and scattering, there has been remained room of investigation.
Further, there is a document where, by using a magnetic iron oxide containing one or more elements selected from element group consisting of Mg, Al, Si, P, S, Ca, Cu, and Zn, a hydrocarbon based wax having predetermined values of hydroxyl value and ester value, and styrene-acrylic copolymer resin at the same time, the magnetic iron oxides and the wax are homogeneously dispersed in the toner particles ((Japanese Patent Application Laid-Open No. 2003-122044). In such a toner, degradation or decrease of electrification can be suppressed, and thereby, a magnetic toner enabling stabilized image formation over a long period of durability can be obtained. However, a case where polyester based resin is used as binder resin, has not been considered, and with regard to a case where miniaturizing of toner particles is advanced, there has been room of investigation, yet.
Moreover, a technology is also proposed, where by using a magnetic iron oxide containing one or more elements selected from element group consisting of Al, Si, P, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Zr, Sn, and Pb, and cross-linking polyvinyl resin at the same time, both of the performance of resin and the dispersibility of the magnetic iron oxide are made compatible (Japanese Patent Application Laid-Open No. 2003-221813). In this case, a toner can be obtained, which has stable developing performance and durability, while maintaining the low-temperature fixing property thereof. However, with regard to problems such as tailing when particle size is miniatured, or the like, sufficient investigation has not been done.
Moreover, a magnetic iron oxide has been known, in which magnetite is the main crystal structure thereof and which contains amorphous Al almost homogeneously (Japanese Patent Application Laid-Open No. 2005-170689). Such a magnetic iron oxide is a magnetic material which has a low resistance, a low residual magnetization, a high ratio of FeO, and a good degree of blackness. However, in general, it is required for a toner for electrophotography to have a nearly insulating resistance value, thereby it has been difficult to use such a low resistance magnetic iron oxide.
As mentioned above, in a magnetic iron oxide for magnetic toners, investigation for giving excellent fluidity and environmental stability of charging quantity to the magnetic iron oxide by causing it to contain a different kind of metal has been done, until now, but, under the present situation, there has been room to improve the problems.